# HG changeset patch
# User IBBoard <dev@ibboard.co.uk>
# Date 1506974542 -3600
# Node ID 2acc1ad8d365fd3f019b9bae9d22c4aa92e251e8
# Parent  69eb40c4679872506c1a700fc30544c041be7b8c
Add half-completed sudoku solver

diff -r 69eb40c46798 -r 2acc1ad8d365 3-Prolog/day3-sudoku.pl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/3-Prolog/day3-sudoku.pl	Mon Oct 02 21:02:22 2017 +0100
@@ -0,0 +1,46 @@
+% Create a generic sudoku reader
+
+valid([]).
+valid([Head|Tail]) :-
+    fd_all_different(Head),
+    valid(Tail).
+
+sudoku(Board, X, Y, Solution) :-
+    Solution = Board,
+    Max is X * Y,
+    fd_domain(Solution, 1, Max),
+    board(X, Y, Board),
+    rows(Board, Max, Rows),
+    cols(Board, Max, Cols),
+    valid(Rows),
+    valid(Cols).
+% TODO: Calculate boxes and validate them
+
+board(X, Y, Board) :-
+    Size is X * Y * X * Y,
+    board(Size, Board).
+board(1, [_]).
+board(Size, [_|Board]) :- SmallerSize is Size - 1, board(SmallerSize, Board).
+
+sublist(Start, Length, Input, Output) :- End is Start + Length - 1, sublist(Start, End, 1, Input, Output).
+sublist(Start, End, Pos, [Head|TailIn], [Head|TailOut]) :- Pos >= Start, Pos =< End, NextPos is Pos + 1, sublist(Start, End, NextPos, TailIn, TailOut).
+sublist(Start, End, Pos, [_|TailIn], Output) :- Pos < Start, NextPos is Pos + 1, sublist(Start, End, NextPos, TailIn, Output).
+sublist(_, End, Pos, _, []) :- Pos > End.
+
+rows(Board, RowLength, Rows) :- rows(Board, RowLength, 1, Rows).
+rows(Board, RowLength, RowNum, [NewRow|Rows]) :- RowNum =< RowLength, NextRowNum is RowNum + 1,
+    Start is ((RowNum - 1) * RowLength) + 1, sublist(Start, RowLength, Board, NewRow),
+    rows(Board, RowLength, NextRowNum, Rows).
+rows(_, RowLength, RowNum, []) :- RowNum > RowLength.
+
+nth_from_list(Start, N, Input, Output) :- nth_from_list(N, Start, 1, Input, Output).
+nth_from_list(N, Next, Pos, [Head|TailIn], [Head|TailOut]) :- Pos == Next, NewNext is Next + N, NewPos is Pos + 1,
+    nth_from_list(N, NewNext, NewPos, TailIn, TailOut).
+nth_from_list(N, Next, Pos, [_|TailIn], Output) :- NewPos is Pos + 1, nth_from_list(N, Next, NewPos, TailIn, Output).
+nth_from_list(_, _, _, [], []).
+
+cols(Board, ColLength, Cols) :- cols(Board, ColLength, 1, Cols).
+cols(Board, ColLength, ColNum, [NewCol|Cols]) :- ColNum =< ColLength, NextColNum is ColNum + 1,
+    nth_from_list(ColNum, ColLength, Board, NewCol),
+    cols(Board, ColLength, NextColNum, Cols).
+cols(_, ColLength, ColNum, []) :- ColNum > ColLength.
\ No newline at end of file